Tyrosine-specific protein kinases (tyrosine kinases) represent a family of enzymes which catalyze the transfer of the terminal phosphate of adenosine triphosphate to tyrosine residues in protein substrates. The first members of this class to be identified were tyrosine kinases associated with viral genes (termed oncogenes) which were capable of cell transformation (i.e. pp60v-src and pp98v-fps). Later it was shown that there were normal cellular counterparts (i.e. pp60c-src and pp98c-fps) to these viral gene products. A third category of tyrosine kinases to be identified are those termed the growth factor receptors, which includes insulin, epidermal growth factor (EGF), platelet derived growth factor (PDGF), fibroblast growth factor (FGF), and p185HER-2 receptors. All of these tyrosine kinases are believed, by way of substrate phosphorylation, to play critical roles in signal transduction for a number of cell functions.
Though the exact mechanisms of signal transduction have yet to be elucidated, tyrosine kinases have been shown to be important contributing factors in cell proliferation, carcinogenesis, and cell differentiation.
Cell replication can be triggered by the exposure of cells to one or more growth factors, examples of which are FGF, EGF, and PDGF. Such growth factors specifically interact with their corresponding receptors, which receptors comprise an extracellular domain, a transmembrane domain and a cytoplasmic domain which possesses the tyrosine kinase enzymatic activity. The initiation of cellular proliferation is believed to occur when a growth factor binds to the extracellular domain of its receptor at the cell surface. This growth factor-receptor binding induces receptor dimerization which results in receptor autophosphorylation, an increase in enzymatic activity of the receptor and substrate phosphorylation. Recently, a common pathway for signaling from the cell surface to the nucleus has been identified and shown to be utilized by the tyrosine kinase growth factor receptors. This pathway involves the growth factor mediated activation of the ras protein which initiates a protein kinase cascade that leads to the phosphorylation of transcriptional factors that regulate the expression of genes involved in cell division.
Receptor autophosphorylation and the phosphorylation of intracellular substrates are biochemical events which are required for growth factor signaling and cell proliferation. This has been demonstrated by eliminating the protein tyrosine kinase activity of a number of receptors including the EGF receptor (EGFR), the FGF receptor (FGFR) and the PDGF receptor (PDGFR) by site-directed mutagenesis which results in the complete loss of the receptors biological activity. Also, protein kinase inhibitors such as Staurosporin, K252a and the tyrphostins which block receptor tyrosine kinase enzymatic activity prevent intracellular signaling and cell proliferation. These studies confirm the essential role of tyrosine phosphorylation in signaling by the growth factor receptors and demonstrate that compounds that inhibit tyrosine kinase activity can be used to regulate cell proliferation.
Many disease states are characterized by uncontrolled cell proliferation. These diseases involve a variety of cell types and include disorders such as cancer, psoriasis, pulmonary fibrosis, glomerulonephritis, atherosclerosis and restenosis following angioplasty. The utility of tyrosine kinase inhibitors for the treatment of such disorders has been demonstrated in a number of in vivo studies. Tyrosine kinase inhibitors with selectivity for the EGFR family have been shown to block tumor formation in animals, thus demonstrating their potential usefulness for directly suppressing tumor cell growth in the treatment of human cancer, especially breast carcinoma. Also, tumor metastasis and its associated angiogenesis has been shown to be inhibited by preventing the activation of the vascular endothelial growth factor receptor tyrosine kinase which indicates a utility for tyrosine kinase inhibitors in blocking separate events that occur during carcinogenesis.
In experimental models of glomerulonephritis, a 20-fold increase in PDGFR expression is associated with mesangial cell proliferation. Neutralization of PDGF which prevents the activation of its tyrosine kinase receptor limits the amount of renal degeneration which normally occurs. These studies demonstrate that a tyrosine kinase inhibitor which blocks PDGFR could have potential for the treatment of human glomerulonephritis.
One major unsolved problem of interventional cardiology is restenosis following coronary angioplasty. Of the nearly 400,000 angioplasties currently performed in the United States each year, 30-40% fail within the first year due to restenosis. The process of restenosis involves the reocclusion of an atherosclerotic artery which in many cases is due to the proliferation of smooth muscle cells which is mediated by growth factors such as PDGF and FGF. In animal models of restenosis, antibodies which block the activation of PDGF or FGF receptor tyrosine kinase activity prevent smooth muscle cell proliferation and the formation of neointima. These studies indicate that tyrosine kinase inhibitors that block PDGF or FGF receptor function could have utility in treating human restenosis.
Currently the chemotherapy of cancer makes use of inhibitors of DNA synthesis (e.g. adriamycin, fluorouracil) and compounds which disrupt the cytoskeleton (vinblastine). These compounds are highly toxic since their inhibitory activity is not limited to cancer cells, with the distinction, however, that tumor cells are more readily attacked by the aforesaid inhibitors because these cells divide more rapidly and their DNA metabolism is consequently more active. A few types of cancers are treated with specific hormone derivatives. These cases, however, are the exception and the chemotherapeutic treatment for the majority of the various types of cancer is non-specific.
In the early 1980's it became apparent that 20 to 30 percent of cancers express characteristic oncogenic products which are growth factor receptors or their mutated homologs, and which exhibit protein tyrosine kinase (PTK) activity. The PTK activity is intrinsic to the receptor or its oncogene homolog and influences the cell proliferation via its PTK domain. Furthermore, each of these receptors (normal or mutated) exhibits a characteristic PTK activity with a distinct substrate specificity. One of these receptors is EGFR and its oncogenic homolog V-ERB-B.
As a result of the above-described developments regarding the PTK activity of growth factor receptors, it has been proposed to treat cancer by means of various chemical substances capable of inhibiting the PTK activity of EGF. See, for example, Japanese patent Nos. 62-39523, 62-39558, 62-42923 and 62-42925. For example, aforementioned Japanese Laid-open Patent No. SHO 62-39558 discloses alpha-cyano-2,5-dihydroxycinnamamide as the active compound in compositions effective as PTK inhibitors.
The use of cinnamyl malononitrile and various benzylidene malononitrile compounds as tumor growth inhibitors is disclosed in Gal et al., Studies on the Biological Action of Malononitriles. I. The Effect of Substituted Malononitriles on the Growth of Transplanted Tumors in Mice, Cancer Research, 12:565-72, 1952.
Yoshida, et al., Japanese Patent Appn. No. 49100080 describes 3-aminopyrazole derivatives that are said to have anti-inflammatory and analgesic effects.